The methods for visually identifying leaking points on subsea pipelines are predominantly, the use of underwater inspection divers and the application of Remotely Operated Vehicles (ROV) equipped with visual and/or several of acoustic/fluorescent/hydrocarbon sensory detection tools. Detecting the leaking point is important because it is a prerequisite to inspections and subsequent actual repair activity.
In muddy water, divers rely on the sensory of the exiting plume of leaking pressure containments such as pipelines to identify the point of leak. The principle is that the leak comes from the base origin of the plume. It is believed that this approach is most exact in all sea conditions and underwater visibility states. The growth in technology requires that a new approach be made in utilizing this phenomenon.
State of the art technology does not solve the existing problems of identifying exact leaking points of structures, such as pipelines, independent of water clarity and by using the effect of plumes.
The limitation with the state-of-the-art technology is considered to be as follows: Search for leaking points by divers in unclear water is achieved by hand feelings of plume exiting from the pipeline break. This procedure has its safety limitations in hazardous hydrocarbon plume. On the other hand, an ROV installed with the best optical camera would see inadequately in muddy water. The poor underwater visibility problem could be due to natural condition of the water (rain sweeps, tidal actions, etc.) or by the action of ROV's thrusters on the subsea bottom in case the seabed is of sediment soil that clouds the visibility.
The present most advanced technology for identification of leaks in marine pipelines and inspection is the use of various forms of acoustic/sonic systems. Acoustic or magnetic flux systems could also be used on intelligent pigs running through the pipeline system. Other systems are hydrocarbon leak detectors that are sensitive to hydrocarbons and the fluorescence techniques. The acoustic and magnetic flux systems require expert interpretations of acquired data and are relatively expensive to operate. The systems are also prone to errors in some cases, for instance, noise from thrusters or sound from adjacent subsea facilities could mislead an acoustically operated leak finder. It is noted that acoustic close range detection of underwater objects is more difficult when the objects are buried in the seabed.
Sediments generate high backscattering noise due to heterogeneous scatters within the sediments clouding the object. The acoustic wave attenuation in sediments is also much higher than in water. Also some low pressure, large breaks in oil pipelines are low acoustic generators and therefore may not be found. For old and aged pipelines brittle fracture propagation can result, in case of the use of high pressure in running or operating pigs in the pipelines. Pigs can abnormally be trapped in the pipeline complicating the problem. The fluorescent and the hydrocarbon leak detectors are difficult to use in very poor underwater visibility conditions. Even in clear water, the applications of fluorescence or hydrocarbon detection sensors would require to sniff close to the suspected leak area. Water waves and currents can misguide the interpretation, especially in unclear water.
In our present innovation, identification of leaking point is made by tracing the signature of the plume generated by a minimal low internal containment pressure within the leaking structure. It has the capability to operate independent of water clarity. It does not require expert interpretation as it is visually tracking the exiting plume from the pipeline. It can use cheap real time technology in the identification process.
Identification, Inspection and Clamping (IIC) Leaking Pipelines Installed in Unclear Water Using an ROV Platform
When the leak has been identified, pipeline repair activity in general requires a range of planning and investigations prior to the actual repair. This includes but is not limited to investigation of the damage, the pipe condition, consequences for the pipeline operation and planning of uncovering and seabed preparation. For instance, the mechanical pressure clamps are usually considered for temporary repairs; however, many subsea clamps are often not replaced and become a permanent repair subject to regular inspection, in particular when the pipeline inspection would also be difficult to implement in all clock positions of the pipeline where underwater visibility is poor. According to DNV-RP-F116, a close visual inspection is the best available method for detecting all threats and for providing the best understanding of the pipeline's damaged conditions. DNV-RP-F116 is a recommended practice for integrity management of submarine pipeline systems. Other situations include cofferdams and pipeline beach pull installations where polyethylene or similar wraps on pipeline weld joints could get damaged without notice due to unclarity of the water condition in the shallows.
A diverless technology of identification, dose visual inspection and repair of leaking pipelines under such unclear water condition is presently not developed. There is presently no method that combines detection, inspection and repair on a single platform in all pipeline leak positions and in all conditions of water clarity.
The limitation with the state-of-the-art technology is considered to be as follows: If the exact point of leak is not found and inspected, adequate repair using remotely operated system is almost impossible. Inspection in unclear water in shallow is often carried out by ‘hand feelings’ by underwater divers. The results for pipeline leak repairs are trial and error attempts and a repair-leak-repair cycle often results, causing continued pollution to the environment. For an ROY equipped with fluorescent and hydrocarbon leak detectors, operation in muddy water is a challenge that needs to be dealt with. As described earlier, even in clear water, the applications of fluorescence or hydrocarbon detection sensors would require sniffing close to the suspected leak area. There is no known ROY platform that identifies and enables close visual inspection and, perhaps, effect repair of leaking structures in muddy water condition.
In the present invention, a common platform for identification, inspection and clamping the pipeline leak is presented (the IIC concept). It has the capability to operate independent of water clarity. It does not require expert interpretation as it is visually inspecting the broken structure of the pipeline. It can also use cheap real time technology in the inspection process.
In a particular aspect of the present invention it includes a flooding box, a digital video camera and illumination lamps. This device can also be used independent of an ROV, e.g. as a hand held tool by divers. The invention does not see the differences and sources of unclarity, it displaces whatever the unclear water is with pressured-clear water that the camera can see through.
In a first aspect the present invention defines an apparatus for close visual inspection of containment structures, such as pipelines, in the marine environment, especially in muddy or unclear water, comprising a housing having a chamber that has an open side, the open side being adapted to be placed in sealing engagement against the containment structure to be inspected, a imaging device, such as a camera, situated within the chamber or situated in a sealed compartment with a transparent wall towards the chamber, and a source of clear water for flooding the chamber with clear water.
This apparatus is capable of providing a clear view for the imaging device towards the leaking containment so to avoid or reduce the need of post-processing of the image. The image quality can be greatly improved by substantially removing the unclear water between the imaging device and the containment.
Preferably, a light source is arranged within the chamber or in a sealed compartment with a transparent wall towards the chamber. This enables the imaging device to see the surface also in dark waters, such as at deep waters or in muddy waters.
The chamber is preferably generally shaped to form a complementary interface with a pipeline. Thereby the unclear water can be replaced by clear water also very close to the pipeline.
In an alternative embodiment the chamber comprises a first part extending over about half the circumference of a cylinder, at least one second part that extends over less than half the circumference of the cylinder, the second part being coupled to the first part via a flexible casing, such as a bellows, so that the second part can be moved, e.g. hingedly, relative to the first part along the circumference of the pipeline. Thereby it is possible to circumscribe a large portion of the circumference of the pipeline and identify leaks over a larger extent of the pipeline.
Preferably, the first part, the at least one second part and the casing, when fully extended, cover the whole circumference of the pipeline. Thereby it is possible to identify leaks all around the circumference of the pipeline.
Even more preferably, the apparatus is arranged on an ROV or similar, which will provide diverless access to containment structures.
In a preferred embodiment, an exit port having a valve is in communication with the chamber in order to expel unclear water from the chamber.
In another aspect of the invention it provides a method for performing close visual inspection of containment structures, such as pipelines, in the marine environment, especially in muddy or unclear water, comprising forming an envelope of clear water near the outer surface of the containment structure, placing an image device within or close to the envelope of clear water, so that the image device has a substantially unobstructed view of the surface, and communicating image data from the image device to a topside facility.
This method will provide a clear view from the imaging device to the containment structure.
In a preferred embodiment, the envelope of clear water is created within a chamber in a housing having an open side towards the structure to be inspected. This makes it easier to uphold the envelop of clear water over a prolonged time.
By having the supply of clear water continuous, the envelope can be upheld over a very long time.
In a third aspect the invention provides an apparatus for identification of exiting substance from broken or leaking underwater equipment, such as a pipeline, comprising a housing defining a chamber with a water permeable side that is adapted to face downward during use, and thereby being exposed to the exiting substance, a gas pressurizing device for creating a gas/water interface within the housing, and an imaging device arranged above the water surface of the gas/water interface, the imaging device being adapted to image the water surface.
This apparatus is capable of detecting the plume of outflow from a leak. When the outflow disturbs the water/gas interface, the imaging device will see a different picture than if the water surface is relatively calm. The more the surface is disturbed, the stronger the impact of the plume is. This effect can be used to find the origin of the plume.
In a preferred embodiment the imaging device is at least one infra-red camera. An infrared camera has proved to provide a better recognition of the disturbance of the surface than a visual light camera.
By having the apparatus being carried by an ROV, it is easier to follow the plume towards its origin.
In a fourth aspect of the present invention it provides a method for identification of exiting substance from broken or leaking underwater equipment; such as a pipeline, wherein a housing containing an imaging device is submerged to a position above the underwater equipment, that a gas/water interface is created within the housing, that the gas/water interface is being exposed to the exiting substance so that presence of exiting substance may disturb the gas/water interface, and that the imaging device images the gas/water interface in order to detect if the gas/water interface is being disturbed.
This method makes it possible to detect the plume of outflow from a leak. When the oufflow disturbs the water/gas interface, the imaging device will see a different picture than if the water surface is relatively calm. The more the surface is disturbed, the stronger the impact of the plume is. This effect can be used to find the origin of the plume.
In a preferred embodiment, the housing is moved to maximise the disturbance and thereby locate the approximate origin of the leak causing the exiting substance when a disturbance of the gas/water interface is being detected.
Preferably, the gas/water interface is imaged in infra-red light, which has proved to be superior over visible light.
By attaching the housing to an ROV, the method can be used on greater water depths and it will be easier to follow the plume towards its origin.
In a fifth aspect the invention provides a clamp for sealing a leak in a pipeline, comprising two halves that are arranged to be connected around a pipeline, wherein each half comprises a double shell having an inner and an outer shell, whereby the space between the shells may be filled with a filler, such as concrete, epoxy or similar.
This will provide a clamp that is relatively easy to install but also can be used to permanently seal the leak.